Update GetContractStateAttribute to take a Contract instead of contract hash

pkg/core/blockchain.go

@@ -1,14 +1,10 @@
 package core
 
-type Contract struct {
-	Attributes ContractAttributes
-}
-
 type Blockchain interface {
 	GetBlockByNumber(blockNumber int64) Block
 	SubscribeToBlocks(blocks chan Block)
 	StartListening()
 	StopListening()
 	GetContract(contractHash string) (Contract, error)
-	GetContractStateAttribute(contractHash string, attributeName string) (interface{}, error)
+	GetAttribute(contract Contract, attributeName string) (interface{}, error)
 }

pkg/core/watched_contract.go

@@ -5,6 +5,11 @@ type WatchedContract struct {
 	Transactions []Transaction
 }
 
+type Contract struct {
+	Attributes ContractAttributes
+	Hash       string
+}
+
 type ContractAttribute struct {
 	Name string
 	Type string